In a first prior art presented by the present applicant, in particular in the application EP 1.087.652, a description has already been given of an improvement to electronic assemblies with heat sink. In such assemblies, a relatively rigid printed circuit or card is associated, by means of a heat-conducting material, with a metallic piece or sole plate which makes it possible to discharge the thermal energy dissipated on the substrate of the printed circuit. In particular, in this first prior art, the metallic sole plate has a stud for fixing to the printed circuit through a drilling therein so that, when the stud is deformed by means of a tool during assembly, the printed circuit and the sole plate are fixed to each other, on the one hand, and a thermal coupling of the printed circuit and metallic sole plate by means of the heat-conducting and electrically insulating material is effected, on the other hand.
Unfortunately, this first prior art introduces several problems. In particular, between the printed circuit and the aluminium radiator, a material with two components, one of which is based on silicone with a filler whilst the other is a screen based on glass fibres, is compressed in a controlled or mastered fashion. The function of the first material is to produce heat conduction. The function of the second material is to effect electrical insulation. More particularly, the dual-component material fills the empty space between the metallic sole plate and the printed circuit.
The electrical earthing between the metallic sole plate and a provided conductive part of the printed circuit is provided by riveting the printed circuit to the sole plate by means of the aforementioned stud.
As a result the use of such a dual-component material is complex and has a high cost during mass production. In a second prior art, the electrical insulation function is provided by raising the printed circuit with respect to its radiator, by a sufficient value to guarantee electrical insulation or thermal conduction through the layer of glass fibres. The hot zones of the printed circuit receive a thin single-phase multilayer adhesive on the bottom face. A layer of copper is provided for thermal conduction whilst a layer of the “Kapton” type is provided for electrical insulation. Contact between the printed circuit on the one hand and the radiator on the other hand is provided solely in the hot zone by a thermal paste which is not electrically insulating and which fills the empty space between the radiator and the printed circuit. This paste makes it possible in particular to achieve a compensation for the geometric tolerances of the mechanical parts. The positioning of the printed circuit is provided by the centring studs on the radiator. Its holding and fixing are provided by the crushing of elastomeric pads fixed in the cover of the module. The cover makes it possible to execute a support for the printed circuit on the face of the housing. The electrical earthing is provided by tin balls which are crushed on a conductive part, provided for this purpose, of a printed circuit when the cover of the module is crimped on its body proper.
In a third prior art, the electrical insulation is also provided by a layer of air. However, the hot areas of the printed circuit benefit from thermal dissipation by means of a dual-component material as in the first prior art. The printed circuit is fixed to the radiator by a screw and the solution of electrical earthing is once again executed by means of tin balls.
All these three aforementioned prior arts therefore propose solutions with a high cost. Because of the dissociation of the heat conduction and electrical insulation functions in particular, there are many parts and also many assembly techniques. There are therefore no possible optimisations of the manufacturing process.
Contrary to this, the invention concerns an electronic assembly with a heat sink that comprises essentially a printed circuit and a housing that can serve for the thermal conduction and/or for the electrical insulation and which comprises a complex interface layer.